Chipper knives of the above type are in operation subjected to very great forces. Since it is advantageous for economical reasons if each chipper knife can be operated as long as possible between each replacement or regrinding and the next, it is desirable for each chipper knife to have a maximum service life. At the same time it is, also for economical reasons, above all in the case of replacement knives that are replaced and not reground after wear, desirable for each chipper knife to contain a minimum of material, that is to be manufactured at as low a cost as possible. Thus, it is as a rule not an alternative to make the knives heavily dimensioned and reinforced in order to obtain a long service life.
While striving to achieve the optimal total economy of a knife system for chippers, it is also important to find a method of manufacture which provides rational manufacture and high quality.
As a rule, it is desirable to make blanks for the chipper knives with maximum dimensional accuracy so that only a minimum of reworking will be necessary. This results in a reduction of the consumption of materials, the time required for reworking and the costs of machinery and tools for reworking. The blanks can be made by a suitable method, such as rolling, cold drawing, powder metallurgy, forging or casting. It is optimal if the blanks can be made which such high dimensional accuracy that reworking can be limited to slight sharpening of the cutting edges, or alternatively that, in addition, only certain limited portions of the chipper knives, such as abutment surfaces for fastening the chipper knives in the chippers, are subjected to reworking. In sharpening of the chipper knives, it is advantageous if this can be limited to merely a narrow edge portion next to the cutting edge, but it may be difficult to define such a narrow working area so as to achieve a particularly aesthetically good result.
In many cases, it is however still desirable to rework substantially all surfaces of a chipper knife for sufficient dimensional accuracy. When manufacturing chipper knives in which one or both of the major surfaces have a profiled shape in cross-section, that is have grooves or ridges in the longitudinal direction of the chipper knife, it has been found that a very rational method of reworking all surfaces of a chipper knife involves, for instance, deep-feed grinding or pendulum grinding of substantially the entire width of the major surface in the longitudinal direction of the chipper knife. In such a method of manufacture, first a blank is made, by means of a suitable method, for instance metallurgy, cold drawing, powder metallurgy, forging or casting, the blank having basically the desired shape but with a slight oversize. By subsequent grinding, which is carried out by means of a rotating grinding wheel having the desirable cross-sectional profile, and moving the chipper knife and the grinding wheel, during simultaneous rotation of the grinding wheel, relative to each other along the entire longitudinal extent of the chipper knife, the final shape with correct dimensions is achieved. However, such grinding suffers from the drawback that the chipper knit obtains randomly located working stripes in the longitudinal direction of the chipper knife which per se are shallow but nevertheless are important to the service life and operation characteristics of the chipper knife. Such working stripes will extend parallel to the cutting edge, that is perpendicular to the chipping direction, and thus form small indications of fracture which may result in the chipper knife having a slightly lower resistance to the chipping forces acting on it. The working stripes also increase the chipper knife's friction on the wood surfaces and thus add to the increased consumption of energy and can influence the average size of the chips.